Objective, camera and system adapted for optogenetics comprising such objective

ABSTRACT

The present invention concerns an objective (10) for imaging an object field of view of 10° onto an imager (12), the objective (10) comprising in order of the propagating direction: —a first lens unit (U1) comprising several lenses, the first lens unit (U1) having a positive first focal length and a first dimension inferior to 15 millimeters, —a bending mirror (M) adapted to bend at a 90° angle, —a liquid lens (LL), and —a second lens unit (U2) comprising several lenses, the second lens unit (U2) having a positive second focal length and a second dimension, the ratio between the first focal length and the second focal length being comprised between 1.0 and 2.0 and the ratio between the first dimension and the second dimension being superior or equal to 2.

TECHNICAL FIELD OF THE INVENTION

The invention relates to an objective for imaging an object field ofview of 10° onto an imager. The invention also concerns an associatedcamera and an associated system adapted for optogenetics.

BACKGROUND OF THE INVENTION

The retina is composed of photoreceptors, which are highly specializedneurons that are responsible for photosensitivity of the retina byphototransduction, i.e. the conversion of light into electrical andchemical signals that propagate a cascade of events within the visualsystem, ultimately generating a representation of world. In thevertebrate retina, phototransduction is initiated by activation oflight-sensitive receptor protein, rhodopsin.

Photoreceptor loss or degeneration, such as in case of retinitispigmentosa (RP) or macular deneneration (MD), severely compromises, ifnot completely inhibits, phototransduction of visual information withinthe retina. Loss of photoreceptor cells and/or loss of a photoreceptorcell function are the primary causes of diminished visual acuity,diminished light sensitivity, and blindness.

Several therapeutic approaches dedicated to retinal degenerativediseases are currently in development, including gene therapy, stem celltherapy, optogenetics, and retinal prostheses (Scholl et al., 2016,Science Translational Medicine, 8 (368), 368rv6).

For example it has been proposed to restore photosensitivity of theretina of a subject by controlling activity of defined populations ofneurons without affecting other neurons in the brain by gene- andneuroengineering technology termed optogenetics. In contrast totraditional gene therapy that attempts to replace or repair a defectivegene or bypass the genetic defect through correction of the proteindeficiency or dysfunction, optogenetic approaches can be used to endownormally non-photosensitive cells in the retina with the ability torespond to light, thus restoring useful vision to the patient. Unlikeretinal chip implants that provide extracellular electrical stimulationto bipolar or ganglion cells, optogenetics-based therapies stimulate thecells from inside the cell.

Optogenetics (Deisseroth. Nat Methods 8 (1): 26-9, 2011) refers to thecombination of genetics and optics to control well-defined events withinspecific cells of living tissue. Optogenetics It consists in (i)genetically modifying target cells in order to render them sensitive tolight by the expression of exogenous photoreactive proteins in cellularmembrane and (ii) providing illuminating device able to provide light tosaid photoreactive proteins.

Examples of exogenous photoreactive proteins are provided inWO2007024391, WO2008022772 or WO2009127705 which describe the use ofopsin genes derived from plants and microbial organisms (e.g.archaebacteria, bacteria, and fungi) encoding light-activated ionchannels and pumps (e.g. channelrhodopsin-2 [ChR2]; halorhodopsin[NpHR]), engineered for expression in mammalian neurons and which can begenetically targeted into specific neural populations using viralvectors. When exposed to light with appropriate wavelength, actionpotentials can be triggered in opsin-expressing neurons conferringthereby light sensitivity to these cells. Similarly, WO2013071231discloses new channelrhodopsins, Chronos and Chrimson, which havedifferent activation spectra from one another and from the state of theart (e.g., ChR2/VChR1), and allow multiple and distinct wavelengths oflight to be used to depolarize different sets of cells in the sametissue, by expressing channels with different activation spectragenetically expressed in different cells, and then illuminating thetissue with different colors of light.

Optogenetics is an extremely powerful tool for selective neuronalactivation/inhibition which can, for example, be used to restore neuralfunctions in living animals, including humans (Boyden et al., 2005,Nature Neuroscience 8 (9): 1263-68), particularly in the eye (Busskampet al., 2012, Gene Therapy 19 (2): 169-75).

Nevertheless, it has been shown that selected wavelengths of light shallbe close to the optimal wavelengths of the photoreactive proteins (Nagelet al. 2003, Proceedings of the National Academy of Sciences 100 (24):13940-45, Klapoetke et al. 2014, Nature Methods 11 (3): 338-46) and thatthese photoreactive proteins have a very low sensitivity to light(Asrican et al. 2013, Front Neural Circuits, 2013, 7:160; Busskamp etal. 2012, Gene Therapy 19 (2): 169-75). Therefore in order to obtainminimum level of protein activation by light, the intensity of lightreceived by the target cell or protein shall be above a minimum value(Barrett et al., 2014, Visual Neuroscience 31 (4-5): 345-354). As aconsequence, an external device providing sufficient irradiance at theright wavelength is mandatory.

Alternatively, it has been proposed to restore at least partially visionin these patients with visual prosthesis systems. These systems arecomprising a retina implant which are helpful tools for at leastpartially re-establishing a modest visual perception and a sense oforientation for blind and visually impaired users by exploiting saidfact that although parts of the retinal tissue have degenerated most ofthe retina may remain intact and may still be stimulated directly bylight dependent electrical stimuli. Typically, retina implant isimplanted into the patient's eye, effecting electrical excitation of theremaining neuronal cells upon light stimulation. When being stimulated,these remaining neuronal cells convey the artificially inducedelectrical impulses to the visual part of the brain through the opticnerve.

Retinal implants can be broadly divided into two categories: epi- andsub-retinal (Lin et al., 2015, Retinal prostheses in degenerativeretinal diseases, J Chin Med Assoc.; 78(9):501-5). Epi-retinal devicesare placed on or near the inner surface of the retina, i.e. the side ofthe retina which is first exposed to incident light and along which thenerve fibers of the ganglion cells pass on their way to the optic nerve.Epi-retinal implants typically comprise a chip with a plurality of pixelelements capable of receiving an image projected by an extraoculardevice (typically a camera and a microelectronic circuit for decodingincident light) on the retina through the lens of the eye, forconverting the image into electrical signals and for further conveyingthe signals into electrical stimuli via a plurality of stimulationelectrodes to stimulate the retinal cells adjacent the chip, in order toreconstruct or improve vision of blind or partially blind patients. Incontrast, sub-retinal devices are placed under the retina, between theretina and the underlying retinal pigment epithelium or other deepertissues. Currently available sub-retinal technologies rely on theimplantation of a single, rigid and typically planar chip. It has beenfurther shown that it is desirable to be able to implant more than onechip in order to cover a large visual field (Lee et al. (2016).Implantation of Modular Photovoltaic Subretinal Prosthesis. OphthalmicSurgery, Lasers and Imaging Retina, 47(2), 171-174).

Retinal prostheses and optogenetic therapies rely on two maincomponents. The first component engineered on the retina provides lightsensitivity through transducing photons into electrochemical signals:the implant in retinal prosthesis system and light-gated ion channelprotein genetically introduced in the retinal cells in optogenetictherapies. A second component is required to encode visual information(usually acquired with a camera or array of photodiodes) and totranslate it in an input signal required by the former component. Inretinal prostheses, the input signal is an electrical current deliveredby a matrix of active electrodes or a pulse of light capable ofactivating passive components. In optogenetics gene therapy, the inputsignal which is delivered is a pulse of light at the appropriateintensity and wavelength required to activate the optogenetic protein ina defined spatio-temporal manner.

Regardless of the approach used to restore light sensitivity, astimulating device able to encode visual information in real time isrequired.

SUMMARY OF THE INVENTION

The invention aims at providing an objective adapted to be embedded in astimulating device used in a system to restore partially vision on blindsubjects affected by Retinis Pigmentosa.

For this, thanks to his studies, the Applicant has expressed therequirements to be fulfilled by such objective.

First, the objective should have a reduced size, notably inferior to 25millimeters.

Moreover, the objective has to provide a sufficient resolution, inparticular inferior to 30 micrometers (μm).

Furthermore, the objective should provide with an object field of viewof 10°.

The objective should also provide with a tunable focal length enablingto image objects situated above 40 centimeters.

To this end, it is proposed an objective for imaging an object field ofview of 10° onto an imager provided with more than 100 pixels, apropagating direction being defined for the objective, the objectivecomprising in order of the propagating direction a first lens unit, abending mirror, a liquid lens and a second lens unit. The first lensunit comprises a plurality of lenses, the first lens unit having a firstfocal length and a first dimension, the first focal length beingpositive and the first dimension being inferior to 15 millimeters. Thebending mirror is adapted to bend at a 90° angle. The second lens unitcomprises a plurality of lenses, the second lens unit having a secondfocal length and a second dimension, the second focal length beingpositive, the ratio between the first focal length and the second focallength being comprised between 1.0 and 2.0 and the ratio between thefirst dimension and the second dimension being superior or equal to 2.

Thanks to the presence of the bending mirror and the limitation on thefirst dimension, the objective has a reduced size.

The use of a liquid lens provides with an adjustable focal lengthenabling to image objects situated above 40 centimeters.

In addition, the specific architecture with two lens units with positivefocal lengths, the ratio between the first focal length and the secondfocal length being comprised between 1.0 and 2.0 and the ratio betweenthe first dimension and the second dimension being superior or equal to2 enables to obtain an image quality which provides a sufficientresolution for an object field of view of 10°.

The above-mentioned benefits of the architecture of the objective aspreviously described are obtained regardless the definition of lenssequences and aperture stops.

According to further aspects of the invention which are advantageous butnot compulsory, the objective might incorporate one or several of thefollowing features, taken in any technically admissible combination:

-   -   the material of each lens belonging to the first lens unit and        the second lens unit is chosen among only two distinct        materials.    -   This feature enables to reduce the number of lenses involved        while keeping a sufficient image quality. As a result, such        feature also contributes to obtaining an objective with a        reduced size.    -   the number of lenses of the first lens unit and the number of        lenses of the second lens unit is inferior or equal to four.    -   This feature reduces the number of lenses which are present in        the objective, which notably reduce the size of the objective.    -   at least one of the first lens unit and of the second lens unit        comprises a biconvex lens and a concave meniscus.    -   Such feature enables to limit the number of lenses which keeping        a sufficient image quality. This also results in an objective        easier to manufacture.    -   each lens belonging to the first lens unit and the second lens        unit is chosen among only a biconvex lens or a meniscus lens.    -   Such feature enables to limit the number of lenses which keeping        a sufficient image quality. This also results in an objective        easier to manufacture.    -   the first lens unit comprises at least two lenses, the first        lenses in the propagating direction being a convergent lens and        a divergent lens, the ratio in absolute value between the focal        length of the divergent lens and the focal length of the        convergent lens being comprised between 1.8 and 2.2.    -   Such feature enables to obtain in an easier way a good image        quality. This also results in an objective with a reduced size.    -   the first focal length is comprised between 30.0 millimeters and        40.0 millimeters.    -   Such feature limits the focal length of the first lens unit.        This results in an objective with a reduced size.    -   the second focal length is comprised between 20.0 millimeters        and 35.0 millimeters.    -   Such feature limits the focal length of the second lens unit.        This results in an objective with a further reduced size.    -   the second lens unit comprises, in the order of the propagating        direction, a divergent lens and a convergent lens, the ratio in        absolute value between the focal length of the divergent lens        and the focal length of the convergent lens being comprised        between 1.8 and 3.6.    -   The presence of such feature improves the quality of the image.    -   the first lens of the first lens unit has an entrance focal        length and the last lens of the second lens unit has an exit        focal length, the ratio between the exit focal length and the        entrance focal length in absolute value being comprised between        0.7 and 1.0.    -   Such feature enables to obtain a good image quality over the        whole field of 10°.    -   the first lens unit consists of three lenses.    -   Such feature enables to limit the number of lenses which keeping        a sufficient image quality. This also results in an objective        easier to manufacture.    -   the second lens unit consists of two lenses.    -   Such feature enables to limit the number of lenses which keeping        a sufficient image quality. This also results in an objective        easier to manufacture.

The specification also relates to a camera comprising an imager withmore than 100 pixels and an objective as previously described.

It is also proposed a system adapted for optogenetics comprising acamera as previously described.

The above-mentioned system adapted to optogenetics is at least in partintended to be implanted in the eye of a patient. In particular, thecamera of the system is intended to be implanted in the eye of thepatient.

This may lead that the system has to respect quality and safetystandards in order to be implanted in the eye. Moreover, this may leadto delimit structurally the system in terms of size and form in order tobe implanted in the eye.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on the basis of the followingdescription which is given in correspondence with the annexed figuresand as an illustrative example, without restricting the object of theinvention. In the annexed figures:

FIG. 1 shows schematically an objective and an imager, the objectivecomprising a first lens unit and a second lens unit,

FIG. 2 shows a schematic view of the first lens unit of FIG. 1,

FIG. 3 shows a schematic view of the second lens unit of FIG. 1, and

FIG. 4 illustrates a system adapted for optogenetics comprising theelements of FIG. 1.

GENERAL DESCRIPTION OF THE OBJECTIVE

An objective 10 and an imager 12 are represented schematically on FIG.1.

The objective 10 is adapted to image an object field of view of 10° ontothe imager 12.

A propagating direction Z is defined for the objective 10. Thepropagating direction Z is defined as the optical axis of each opticalelement that is part of the objective.

The objective 10 comprises in order of the propagating direction Z afirst lens unit U1, a bending mirror M, a liquid lens LL and a secondlens unit U2.

The first lens unit U1 comprises a plurality of lenses.

The number of lenses of the first lens unit U1 is inferior or equal tofour.

The material of each lens belonging to the first lens unit U1 is chosenamong only two distinct materials.

For instance, two distinct materials are N-BK7 and N-SF11.

The first lens unit U1 has a first focal length f_(U1) and a firstdimension D_(U1).

The first focal length f_(U1) is positive.

According to an example, the first focal length f_(U1) is comprisedbetween 30.0 millimeters (mm) and 40.0 mm.

The first dimension D_(U1) is inferior to 15 mm.

The bending mirror M is adapted to bend at a 90° angle.

A first optical axis OA1 is defined for the first lens unit U1 and thesecond optical axis OA2 is defined for the liquid lens LL and the secondlens unit U2.

The expression “the bending mirror M is adapted to bend at a 90° angle”means that the first optical axis OA1 and the second optical axis OA2are perpendicular.

In the example of FIG. 1, the bending mirror M is a flat mirror which isarranged at 45° with relation to the first optical axis OA1 and thesecond optical axis OA2.

The liquid lens LL is adapted to change its focal length uponapplication of a voltage.

The change of focal length of the liquid lens renders the objective 10adapted to image objects situated at more than 40 centimeters from thefirst lens unit U1.

The second lens unit U2 comprising a plurality of lenses.

The number of lenses of the second lens unit U2 is inferior or equal tofour.

The material of each lens belonging to the second lens unit U2 is chosenamong only two distinct materials.

For instance, two distinct materials are N-BK7 and N-SF11.

The second lens unit U2 has a second focal length f_(U2) and a seconddimension D_(U2).

The second focal length f_(U2) is positive.

The ratio between the first focal length f_(U1) and the second focallength f_(U2) is named the first ratio R1. This can be expressedmathematically as:

${R1} = \frac{f_{U1}}{f_{U2}}$

The first ratio R1 is comprised between 1.0 and 2.5.

Mathematically, this means that:1.0≤R1≤2.5As a specific example, the second focal length f_(U2) is comprisedbetween 20.0 mm and 35.0 mm.

The ratio between the first dimension D_(U1) and the second dimensionD_(U2) is named the second ratio R2. This can be expressedmathematically as:

${R2} = \frac{D_{U1}}{D_{U2}}$

The second ratio R2 is superior or equal to 2. Mathematically, thismeans that:R2≥2

The second ratio R2 is inferior or equal to 3. Mathematically, thismeans that:R2≤3

A specific example of first lens unit U1 is shown on FIG. 2.

In such case, the first lens unit U1 consists of three lenses.

In order of the propagating direction, the first lens of the first lensunit U1 is named first lens L1, the second lens of the first lens unitU1 is named second lens L2 and the third lens of the first lens unit U1is named third lens L3.

The first lens L1 is a convergent lens.

The first lens L1 has a focal length f_(L1).

The focal length f_(L1) is the entrance focal length of the objective.

In addition, the first lens L1 is a biconvex lens.

By definition, a biconvex lens is a lens whose both surfaces are convex.

In this specific example, the first lens L1 is an equiconvex lens withmeans that both surfaces have the same radius of curvature.

The second lens L2 is a divergent lens.

The second lens L2 has a focal length f_(L2).

The second lens L2 is a meniscus, which is a lens with one convex andone concave side. Such kind of meniscus is also named convex-concavelens.

The second lens L2 is, in this case, a negative meniscus.

The ratio in absolute value between the focal length f_(L2) of thesecond lens L2 and the focal length f_(L1) of the first lens L1 is namedthird ratio R3.

The third ratio R3 is comprised between 1.8 and 2.2.

Mathematically, this means that:1.8≤R3≤2.2

The third lens L3 is a divergent lens.

The third lens L3 has a focal length f_(L3).

The third lens L3 is a meniscus.

The third lens L3 is, in this case, a positive meniscus.

A specific example of second lens unit U2 is shown on FIG. 3.

In such case, the second lens unit U2 consists of two lenses.

In order of the propagating direction, the first lens of the second lensunit U2 is named fourth lens L4 and the second lens of the second lensunit U2 is named fifth lens L5.

The fourth lens L4 is a convergent lens.

The fourth lens L4 has a focal length f_(L4).

The fourth lens L4 is a meniscus.

The fourth lens L4 is, in this case, a negative meniscus.

The fifth lens L5 is a divergent lens.

The fifth lens L5 has a focal length f_(L5).

The focal length f_(L5) of the fifth lens L5 is the exit focal length ofthe objective.

In the specific example, the fifth lens L5 is a biconvex lens.

More precisely, the fifth lens L5 is an equiconvex lens.

In another variant, the fifth lens L5 is a meniscus, notably a positivemeniscus.

The ratio in absolute value between the focal length of the fifth lensL5 and the focal length of the fourth lens L4 is named the fourth ratioR4. This can be expressed mathematically as:

${R\; 4} = {\frac{f_{L5}}{f_{L4}}}$

The fourth ratio R4 is comprised between 1.8 and 3.6.

Mathematically, this means that:1.8≤R4≤3.6

The ratio between the exit focal length and the entrance focal length inabsolute value is named the fifth ratio R5.

In the specific case of FIGS. 2 and 3, the fifth ratio R5 is the ratiobetween the focal length f_(L5) of the fifth lens L5 and the focallength f_(L) of the first lens L1 in absolute value.

This can be expressed mathematically as:

${R\; 5} = {\frac{f_{L5}}{f_{L1}}}$

The fifth ratio R5 is comprised between 0.7 and 1.0.

Mathematically, this means that:0.7≤R5≤1.0

The imager 12 is a set of an array of pixels 14 and a cover glass 16.

The array of pixels 14 comprises more than 100 pixels

In the specific example, the array of pixels 14 is an array of 304pixels per 240 pixels.

The array of pixels 14 is, for instance, made in a CMOS technology.

The cover glass 16 is a plane-parallel plate.

The operating of the objective 10 in relation to the imager 12 is nowdescribed.

Any object in the field of view of the objective 10 situated at morethan 40 centimeters from the first lens unit U1 is imaged on the arrayof pixels 14.

More precisely, the object emits a ray whose wavelength is in thevisible range which passes successively through the first lens L1, thesecond lens L2, the third lens L3. This ray is then reflected by thebending mirror M and passes through the liquid lens LL and then thesecond lens unit U2, that is the fourth lens L4 and the fifth lens L5.The ray then propagates to the cover glass and is then collected by onepixel of the array of pixels 14.

This happens for each ray emitted by the object and more generally foreach imaged object when the scene is imaged by the objective 10 incooperation with the imager 12.

The obtained optical performances of such objective 10 are detailed inthe specific examples which are described in the section named“description of specific embodiments”.

It appears from this section that the objective provides with a reducedsize and no use of mechanical apparatus for moving the lens, whichresults in an objective easier to implement. The objective also enablesto provide a sufficient resolution. Furthermore, the objective provideswith an object field of view of 10°. The objective also provides with anadjustable focal length enabling to image objects situated at more than40 centimeters. Therefore, the objective 10 and the imager 12 enable toconstitute a camera which is suitable for be embedded in a stimulatingdevice used in a system to restore partially vision on bling subjectsaffected by Retinis Pigmentosa.

In other words, such camera is adapted to be part of a system adaptedfor optogenetics.

An example of stimulating device 18 incorporating the objective 10 andthe imager 12 is represented on FIG. 4. In such context, the set of theobjective 10 and the imager 12 is a camera 20 which is a visualfrontend.

The stimulating device 18 also comprises a controller 22 and aprojecting unit 24.

The imager 12 is a QVGA ATIS (Asynchronous Time-based Images Sensor)neuromorphic silicon retina. Rather than sending frames at specifictemporal intervals, each pixel of the imager 12 asynchronously sends anevent encoding its coordinates as soon as it undergoes a local change oflight. Events also trigger a dedicated pixel-based circuitry integratinglight through time to compute a corresponding light intensity level.Each pixel therefore behaves asynchronously and in parallel with theothers, without having to wait for a frame to transmit information. Eachpixel sends information only when something new happens locally.

This translates to a low-latency, bandwidth-efficient encoding scheme,which shares the same properties as its biological counterparts; it isin fact possible to replicate in-vitro responses of retinal ganglionscells using this representation. Moreover, as pixels only send changesof information, redundancy is kept low, with obvious benefits for thesubsequent processing layers. This approach contrasts with thetraditional method of sending frames and provides fast, data-drivencontrast detection at a wide range of illuminations.

The use of this imager 14 offers several advantages. In the case ofphotoreceptors restoration, the imager 14 provides fast, high-dynamicrange grey level information. In the case of retinal ganglions cellsactivation, the imager 14 provides a preprocessed contour or eventsignal over a wide intensity range. The imager 14 temporal resolutionalso matches the one of the human retina. Projecting at low temporalresolutions impacts behavioral performance when observing moving stimuliin everyday tasks such as judging speeds, counting objects ordiscriminating numbers.

The projecting unit 24 is a Texas Instrument LightCrafter, controlling alight source and a DLP3000 Digital Micromirror Device (DMD). The DMDcomprises a 608×684 array of mirrors that can switch every 0.7millisecond (ms) between two discrete angular positions named ON andOFF, with the ON position reflecting the incoming light towards thetarget. Processed events are encoded by setting the corresponding mirrorON. Grey levels are encoded in the form of a Pulse Width Modulation.

The processing unit consists of an ARM-based embedded Linux systemrunning an event-based filtering chain. The system communicates with aFPGA board handling the low level management of the imager 14 and of theDMD through a PCI express link and is abstracted in a Linux driver.Information received from the visual sensor is processed by a filteringpipeline and then sent to the DMD for projection. This filter pipelinehandles the noise reduction, the size of the retinal area to beilluminated and the light pulse dynamics for each pixel, so as to complywith the electro-physiological properties of the genetically introducedion channels. The filtering pipeline also handles the algorithms used tostimulate different types of neurons.

In such case, the projecting unit 24 and the controller 22 constitutes adevice for illuminating an object with a controlled light intensity, thelight intensity being controlled when the light intensity fulfills aplurality of conditions to be fulfilled, the plurality of conditionscomprising a condition relative to the intensity at a given time and acondition relative to the dose during a period of time, the devicecomprising a light source adapted to produce a beam whose intensity doesnot fulfill at least one of the conditions to the fulfilled. The devicecomprises a photodiode adapted to measure the intensity of an incidentbeam and an optical system adapted to convey the light from an entranceto at least one exit, the light source, the photodiode and the opticalsystem being arranged so that the device has two distinctconfigurations, an operating configuration in which a first portion ofthe light emitted by the light source is conveyed to the object, and asecond portion of the light emitted by the light source is conveyed tothe photodiode and a control configuration in which, in normaloperating, no light produced by the light source is sent to object norto the photodiode. The device also comprises a controller adapted tocontrol the value of the first portion based on the intensity measuredon the photodiode when the device is in the control configuration andbased on the conditions to be fulfilled.

According to a specific embodiment, one condition to be fulfilled isthat the light intensity at any given time be inferior or equal to amaximum intensity, one condition to be fulfilled is that the lightintensity at any given time be superior or equal to a minimum intensityand one condition to be fulfilled is that the dose during the period oftime be inferior or equal to a maximum value.

Furthermore, the optical system may comprise a plurality of reflectors,each reflector having three positions, a first position in which thereflector reflects the incident beam towards the object, a secondposition in which the reflector reflects the incident beam towards aphotodiode and a third position in which the reflector reflects theincident beam neither to the object nor to the photodiode, thecontroller being adapted to command the position of each reflector, thedevice being in the operating configuration when the controller commandseach reflector to be in the first position or in the second position andthe device being in the control configuration when each reflector iscommanded to be in the third position.

The controller may further be adapted to deduce the number of reflectorsto be moved in the first position based on the intensity measured on thephotodiode when the device is in the control configuration and based onthe conditions to be fulfilled and commanding the deduced number ofmirrors to move in the first position.

In a specific the light source is a matrix of light sources, each lightsource having two states, an unfed state in which the light source emitsno light and a fed state in which the source emits light, the controllerbeing adapted to control the state of each light source.

As a specific example, a plane to be illuminated is defined for theobject and wherein at least one of the light source and the opticalsystem is such that the several independent spatial areas illuminated bydifferent levels of intensity of light can be defined in the plane to beilluminated when the device is in the operating configuration.

Furthermore, the optical system may comprise optical components ensuringthat the point spread function be inferior to 30 μm, preferably inferiorto 25 μm to the system output. As a specific example, the optical systemcomprises a system adapted for correcting optical aberrations, thesystem adapted for correcting optical aberrations being adjustable. Forinstance, the system is adapted for correcting optical aberrations is aliquid lens.

The embodiments and alternative embodiments considered here-above andalso described in the section “detailed description of specificembodiments” can be combined to generate further embodiments of theinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Three embodiments are described in more details in what follows.

Subsequently, numerical data of optic constituting the objective of eachembodiment are given in tables 1, 4 and 7. In the numerical data, thename of the optic is given as well as the unit to which the opticbelongs, its nature, the value of the first radius R_(in), the value ofthe second radius R_(out), the thickness D_(in-out) of the optic, thematerial of the optic, the focal length of the optic and its position.

The nature of an optic is, for a lens, the nature of the lens (biconvex,meniscus or other).

The value of the first radius R_(in) is the value of the radius of thefirst surface of the optic which is impacted by the incoming ray, whichis the entrance radius of the considered optic.

Similarly, the value of the second radius R_(out) is the value of thesecond surface of the optic which is impacted by the incoming ray, whichis the exit radius of the considered optic.

The thickness D_(in-out) of the optic is the distance between the firstsurface (the entrance surface) and the second surface (the exit surface)of the considered optic. The thickness is the distance measured alongthe optical axis defined for the optic.

The focal length is obtained based on the first radius R_(in), thesecond radius R_(out), the thickness D_(in-out) of the optic and theoptical index of the material.

The position is the optic is the distance with the previous optic. Moreprecisely, the position is the distance between the exit surface of theprevious optic and the entrance surface of the considered optic. Thisdistance is measured along the optical axis. This explains why there isno position for the first lens L1. Indeed, there is no reference for thefirst lens L1.

From the values obtained on tables 1, 4 and 7, numerical valuescharacterizing the objective are deduced. The deduced numerical data ofoptic constituting the objective of each embodiment are given in tables2, 5 and 8. More precisely, the deduced numerical data of optic is thefirst focal length f_(U1), the first dimension D_(U1), the second focallength f_(U2), the second dimension D_(U2), the first ratio R1, thesecond ratio R2, the third ratio R3, the fourth ratio R4 and the fifthratio R5.

The first focal length f_(U1) is obtained based on the focal lengths ofthe first lens L1, the second lens L2 and the third lens L3 and on therelative position of these lenses L1, L2 and L3 using, for example, aGullstrand law.

The first dimension D_(U1) corresponds to the sum of the thickness ofthe first lens L1, the distance between the first lens L1 and the secondlens L2, the thickness of the second lens L2, the distance between thesecond lens L2 and the third lens L3 and the thickness of the third lensL3.

The second focal length f_(U2) is obtained based on the focal lengths ofthe fourth lens L4, the fifth lens L5 and on the relative position ofthese lenses L4 and L5 using, for example, a Gullstrand law.

The second dimension D_(U2) corresponds to the sum of the thickness ofthe fourth lens L4, the distance between the fourth lens L4 and thefifth lens L5 and the thickness of the fifth lens L5.

As a reminder, the first ratio R1 is the ratio between the first focallength f_(U1) and the second focal length f_(U2); the second ratio R2 isthe ratio between the first dimension D_(U1) and the second dimensionD_(U2); the third ratio R3 is the ratio in absolute value between thefocal length f_(L2) of the second lens L2 and the focal length f_(L1) ofthe first lens L1; the fourth ratio R4 is the ratio in absolute valuebetween the focal length f_(L4) of the fourth lens L4 and the focallength f_(L5) of the fifth lens of L5, and the fifth ratio R5 is theratio in absolute value between the focal length f_(L1) of the firstlens L1 and the focal length f_(L5) of the fifth lens L5.

The optical performances for each of the embodiment can be foundrespectively in tables 3, 6 and 9.

In each of these tables, the values of the modulation transfer function(MTF) is given for 30 lines per mm on-axis and off-axis (at theextremity of the imaged field of view) are given for a distance of theobject to the objective 10 equal to 40 cm and a distance correspondingto infinity. The corresponding values of the root mean square (RMS)radius of the spot size are given.

Embodiment 1

The embodiment 1 was simulated thanks to a ray-tracing simulator. Suchembodiment 1 only requires three specific lenses, which are the lensesL2, L3 and L4. The other optics are commercially available.

For instance, the first lens L may correspond to the referenceSLB-15B-20PM from OptoSigma (registered trademark), the fifth lens maycorrespond to the reference #63-665 from Edmund Optics (registeredtrademark) and the liquid lens to the reference A58N0 from Varioptic(registered trademark).

TABLE 1 Numerical data of the objective in the first embodiment FocalR_(in) R_(out) D_(in-out) length Position Optic Unit Nature (mm) (mm)(mm) Material (mm) (mm) L1 U1 Biconvex lens 20.76 −20.76 4.8 N-BK7 20.9— L2 U1 Negative meniscus −17.8 −41.7 2.5 N-SF11 −41.5 1 L3 U1 Positive8.11 6.0 4.5 N-BK7 −163.2 0.504 meniscus mirror 5.94 LL Liquid — — 3.45— variable 6.9 lens L4 U2 Negative −7.95 −10.2 1.8 N-SF11 −70.8 2meniscus L5 U2 Biconvex 20.24 −20.24 2.5 N-BK7 20.0 1 lens Cover 2.6glass The index of N-BK7 is 1.5168 and the Abbe number is 64.17. Theindex of N-SF11 is 1.7847 and the Abbe number is 25.68.

The previous results enable to obtain deduced values which are given inthe following table:

TABLE 2 Deduced numerical data of the objective in the first embodimentParameters f_(U1) D_(U1) f_(U2) D_(U2) (mm) (mm) (mm) (mm) R1 R2 R3 R4R5 Value 37.25 13.30 23.70 5.3 1.57 2.51 1.98 3.54 0.95

With the embodiment 1, the following optical performances are obtained:

TABLE 3 Optical performance of the objective in the first embodiment MTFMTF Spot Spot (%) at (%) at size at size at 30 Ip/mm 30 Ip/mm 40 cmInfinity Parameters at 40 cm at infinity (μm) (μm) Value on axis 62 756.5 5 Value off axis 27 45 11 8.75

These optical performances show that the objective 10 according to thefirst embodiment is compliant with the desired requirements, which are:

-   -   having a reduced size,    -   a sufficient resolution,    -   having an object field of view of 10°, and    -   providing with an adjustable focal length enabling to image        objects situated at more than 40 centimeters.

Embodiment 2

The second embodiment was simulated thanks to a ray-tracing simulator.Such second embodiment only requires four specific lenses, which are thelenses L2, L3, L4 and L5. The other optics are commercially available.

For instance, the liquid lens may correspond to the reference A58N0 fromVarioptic (registered trademark).

TABLE 4 Numerical data of the objective in the second embodiment FocalR_(in) R_(out) D_(in-out) length Position Optic Unit Nature (mm) (mm)(mm) Material (mm) (mm) L1 U1 Biconvex lens 22 −22 4.8 N-BK7 22.1 — L2U1 Negative meniscus −18.8 −39.8 2.5 N-SF11 −47.9 1 L3 U1 Positive 8.856.85 4.5 N-BK7 −251.3 0.504 meniscus mirror 5.94 LL Liquid — — 3.45 —variable 6.9 lens L4 U2 Negative −8.4 −14.0 1.8 N-SF11 −31.2 2 meniscusL5 U2 Positive 16.0 −17 2.5 N-BK7 16 .3 1 meniscus Cover 2.6 glass

This results in the following table:

TABLE 5 Deduced numerical data of the objective in the second embodimentParameters f_(U1) D_(U1) f_(U2) D_(U2) (mm) (mm) (mm) (mm) R1 R2 R3 R4R5 Value 35.80 13.30 26.10 5.3 1.37 2.51 2.16 1.90 0.74

With the embodiment 2, the following optical performances are obtained:

TABLE 6 Optical performance of the objective in the second embodimentMTF MTF Spot Spot (%) at (%) at size at size at 30 Ip/mm 30 Ip/mm 40 cmInfinity Parameters at 40 cm at infinity (μm) (μm) Value on axis 68 886.65 2.7 Value off axis 28 18 12.7 14

These optical performances show that the objective 10 according to thesecond embodiment is compliant with the desired requirements, which are:

-   -   having a reduced size,    -   a sufficient resolution,    -   having an object field of view of 10°, and    -   providing with an adjustable focal length enabling to image        objects situated at more than 40 centimeters.

Embodiment 3

The third embodiment was simulated thanks to a ray-tracing simulator.Such second embodiment only requires four specific lenses, which are thelenses L1, L2, L3 and L4. The other optics are commercially available.

For instance, the liquid lens may correspond to the reference A58N0 fromVarioptic (registered trademark).

TABLE 7 Numerical data of the objective in the third embodiment FocalR_(in) R_(out) D_(in-out) length Position Optic Unit Nature (mm) (mm)(mm) Material (mm) (mm) L1 U1 Biconvex lens 19.0 −24.3 4.8 N-BK7 21.4 —L2 U1 Negative −20.75 −52.6 2.5 N-SF11 −45.2 1 meniscus L3 U1 Positive9.5 7.205 4.5 N-BK7 −173.9 0.504 meniscus mirror 5.94 LL Liquid lens — —3.45 — variable 6.9 L4 U2 Negative −8 −11 1.8 N-SF11 −50.8 2 meniscus L5U2 Biconvex lens 19.3 −19.3 2.5 N-BK7 19.1 1 Cover 2.6 glass

This results in the following table:

TABLE 8 Deduced numerical data of the objective in the third embodimentParameters f_(U1) D_(U1) f_(U2) D_(U2) (mm) (mm) (mm) (mm) R1 R2 R3 R4R5 Value 36.60 13.30 25.15 5.3 1.46 2.51 2.11 2.66 0.89

With the embodiment 3, the following optical performances are obtained:

TABLE 9 Optical performance of the objective in the third embodiment MTFMTF Spot Spot (%) at (%) at size at size at 30 Ip/mm 30 Ip/mm 40 cmInfinity Parameters at 40 cm at infinity (μm) (μm) Value on axis 73 836.5 4.4 Value off axis 29 49 11 9.2

These optical performances show that the objective 10 according to thesecond embodiment is compliant with the desired requirements, which are:

-   -   having a reduced size,    -   a sufficient resolution,    -   having an object field of view of 10°, and    -   providing with an adjustable focal length enabling to image        objects situated at more than 40 centimeters.

The invention claimed is:
 1. An objective for imaging an object field ofview of 10° onto an imager provided with more than 100 pixels, apropagating direction being defined for the objective, the objectivecomprising in order of the propagating direction: a first lens unitcomprising a plurality of lenses, the first lens unit having a firstfocal length and a first dimension, the first focal length beingpositive and the first dimension being inferior to 15 millimeters; abending mirror adapted to bend at a 90° angle; a liquid lens; and asecond lens unit comprising a plurality of lenses, the second lens unithaving a second focal length and a second dimension, the second focallength being positive, the ratio between the first focal length and thesecond focal length being comprised between 1.0 and 2.0 and the ratiobetween the first dimension and the second dimension being superior orequal to
 2. 2. The objective according to claim 1, wherein the materialof each lens belonging to the first lens unit and the second lens unitis chosen among only two distinct materials.
 3. The objective accordingto claim 1, wherein the number of lenses of the first lens unit and thenumber of lenses of the second lens unit is inferior or equal to four.4. The objective according to claim 1, wherein at least one of the firstlens unit and of the second lens unit comprises a biconvex lens and aconcave meniscus.
 5. The objective according to claim 1, wherein eachlens belonging to the first lens unit and the second lens unit is chosenamong only a biconvex lens or a meniscus lens.
 6. The objectiveaccording to claim 1, wherein the first lens unit comprises at least twolenses, the first lenses in the propagating direction being a convergentlens and a divergent lens, the ratio in absolute value between the focallength of the divergent lens and the focal length of the convergent lensbeing comprised between 1.8 and 2.2.
 7. The objective according to claim1, wherein the first focal length is comprised between 30.0 millimetersand 40.0 millimeters.
 8. The objective according to claim 1, wherein thesecond focal length is comprised between 20.0 millimeters and 35.0millimeters.
 9. The objective according to claim 1, wherein the secondlens unit comprises, in the order of the propagating direction, adivergent lens and a convergent lens, the ratio in absolute valuebetween the focal length of the divergent lens and the focal length ofthe convergent lens being comprised between 1.8 and 3.6.
 10. Theobjective according to claim 1, wherein the first lens of the first lensunit has an entrance focal length and the last lens of the second lensunit has an exit focal length, the ratio between the exit focal lengthand the entrance focal length in absolute value being comprised between0.7 and 1.0.
 11. The objective according to claim 1, wherein the firstlens unit consists of three lenses.
 12. The objective according to claim1, wherein the second lens unit consists of two lenses.
 13. A cameracomprising an imager with more than 100 pixels and an objectiveaccording to claim
 1. 14. A system adapted for optogenetics comprising acamera according to claim 13.